1. Technical Field
The present invention relates to a linear encoder having an assembly that includes a support on which a scale supporting a measurement graduation is fastened by a fastener. The fastener is embodied in such a way that in case of temperature changes a temperature-dependent linear expansion of the support in relation to the scale is made possible, and wherein the assembly can be fastened by the support on a body to be measured.
2. Background Information
An example of a linear encoder is described in EP 1 004 855 B1. The linear encoder is employed for measuring lengths, as well as travel distances, and is employed in particular in processing machinery for measuring the relative movements of a tool in relation to a workpiece to be processed, in coordinate-measuring machinery, and increasingly in the semiconductor industry.
The linear encoder has an assembly that includes a support and a scale. The support is provided for stabilizing the scale and thereby making it easier to manipulate the scale. For attaching the scale to a body to be measured, the support has a fastener on the body to be measured. For example, the scale can include bores to be used in conjunction with screws for screwing the scale to the body to be measured. The support includes a material whose coefficient of expansion differs from that of the scale. The scale is attached to the support by fasteners in order to allow a displacement as free as possible of friction between the support and the scale, caused by temperature changes as a result of different linear expansions of the support and the scale.
The scale is rigidly connected with the support at a single location, also called a fixed point. This rigid coupling takes place by a positive connection, wherein positive connection is known in the art as “form closure.” In this position (viewed in the measuring direction) a rigid fastening of the support on the body to be measured is also provided.
This type of construction has the disadvantage that distortions of the support, for example during screwing the support to the body to be measured, or in case of temperature changes, can result in a displacement of the fixed point, which results in inaccurate measurements.